Quick cook dehydrated vegetables

ABSTRACT

Quick-cooked dehydrated vegetables having a moisture content of about 12% or less which have been compressed, but maintain a substantially intact cellular structure, and which on being placed in water at a temperature of 90° C. to 100° C. are capable of rehydration substantially to their original fresh dimensions, and are of edible tenderness and texture instantly or within five minutes, are described. Also described are processes for the production of a dehydrated, rapidly rehydrating vegetable product by compression of a partially dehydrated vegetable product.

FIELD OF THE INVENTION

This invention relates to quick cooking vegetables, more particularlyquick cooking dehydrated vegetables.

BACKGROUND OF THE INVENTION

Dehydrated vegetables are important items of commerce. They areprocessed fresh vegetables in shelf-stable form and are used extensivelyin the food industry, particularly to provide colour, flavour andnutritional benefits to a wide variety of dry packaged foods.

In the packaged food industry they are especially important in cupsoups, cup noodles and in packaged rice and pasta dishes. These areconvenience products and quick cook times are regarded as important. Inmany products the cooking directions call for the addition of boilingwater only, without further cooking. The use of vegetables in theseproducts may require the use of expensive freeze-dried vegetables, orelse very small dehydrated vegetable pieces. As the hot product may takeabout two to three minutes to cool sufficiently to be comfortable toconsume, it is desirable that the vegetables be sufficiently rehydratedwithin this time. Conventional dehydrated vegetables, even small pieces,are usually still hard and gritty after three minutes due to incompleterehydration. Freeze-dried vegetables are expensive and often stillspongy in texture after two to three minutes. For products cooked in themicrowave or on stove top, a desirable cook time is as short aspossible, preferably below five minutes. It is therefore highlydesirable to have an economical dehydrated vegetable component thatrehydrates quickly enough to be pleasant to consume after boiling wateris added and allowed to stand for two to three minutes, and rehydratesback to a natural tasting piece of vegetable.

Alternate quick-cooking dehydrated vegetables such as solute addedproducts (U.S. Pat. No. 4,683,141) or puffed vegetables (U.S. Pat. No.3,038,813) have been described, but neither appear to give productssufficiently quick-cooking for many convenience packaged foods.

The term “vegetable” as used in this application refers to fresh orfrozen fleshy vegetables such as carrots, peas, peppers, tomatoes, sweetcorn and such, but does not refer to dry products of vegetable originsuch as wheat, corn, dry legumes and such, and dried fruits such asapple.

U.S. Pat. No. 3,408,209 describes subjecting explosion puffed vegetablesas described in U.S. Pat. No. 3,038,813 and compressing them for thepurpose of reducing their bulk for packaging purposes. There is no claimthat this process reduces cooking time.

There is a need for a dehydrated vegetable product with a cook time offrom instant to about five minutes, which is not gritty, has a pleasanttexture and mouth feel, and is inexpensive to prepare. It is to beunderstood that cook time refers to the time at which the vegetablepiece is substantially rehydrated to its size prior to dehydration andis free from hard or gritty centres.

The result may be achieved by mechanically compressing partiallydehydrated vegetable pieces, as by passing between the rolls of a rollermill or by other means, to an extent whereby the pieces are noticeablyflattened, but not to such an extent that the texture of the rehydratedproduct is unacceptably altered from that of a rehydrated vegetablepiece which had not been compressed. The vegetable is then further driedto a moisture content of about 5% or lower, or in the case ofintermediate moisture products, to a higher level. Surprisingly, thecompressed vegetable pieces, when rehydrated, return to much the samesize and shape as the original pieces prior to initial dehydration butin a significantly shorter time than untreated dehydrated vegetables.

SUMMARY OF THE INVENTION

In one aspect, this invention provides a dehydrated vegetable productwhich comprises a vegetable piece having a moisture content of about 12%or less which has been compressed preferably in one dimension but stillhas a substantially intact cellular structure, and which on being placedin water at a temperature of 90° C. to 100° C. is capable of rehydrationsubstantially to its original fresh dimension and is of edibletenderness and texture instantly or within five minutes.

In another aspect, this invention provides a dehydrated vegetableproduct prepared by partially dehydrating vegetable pieces to a moisturecontent from about 8% to about 30%, compressing the vegetable pieces,and thereafter further dehydrating the vegetable pieces to a moisturecontent of about 12% or lower.

In a further aspect, the invention provides a process for thepreparation of a dehydrated, rapidly rehydrating, vegetable product bycompression of a partially dehydrated vegetable product.

DETAILED DESCRIPTION OF THE INVENTION

This invention is concerned with quick-cooked dehydrated vegetables andin accordance with one aspect of the invention a dehydrated vegetableproduct which comprises a vegetable piece having a moisture content ofabout 12% or less which has been compressed but still has asubstantially intact cellular structure, and which on being placed inwater at a temperature of 90° C. to 100° C. is capable of rehydrationsubstantially to its original fresh dimension and is of edibletenderness and texture instantly or within five minutes.

In accordance with a further aspect of this invention there is provideda dehydrated vegetable product prepared by partially dehydratingvegetable pieces to a moisture content from about 8% to about 30%,compressing the vegetable pieces, and thereafter further dehydrating thevegetable pieces to a moisture content of about 12% or lower.

The term “vegetable” as mentioned above refers to fleshy vegetables,such as carrots, peas, peppers, tomatoes, sweet corn, onion, squash,chillies, zucchini, mushroom, cabbage, celery, green beans, beetroot,pumpkin, and the like, and including frozen fresh vegetables, butexcluding dried products of vegetable origin such as wheat, corn, drylegumes and such, and dried fruits such as apples, apricots and grapes.A “vegetable piece” may comprise a small vegetable in its totality, suchas a pea, small tomato, sweet-corn kernels, mushroom and the like. Theterm “vegetable piece” also includes a vegetable which has been cut to asize suitable for use in the food industry, for example pieces of 10×4×4mm.

In one embodiment, the vegetables may be washed, cut to an appropriatesize as needed, optionally blanched and placed in a dehydrator, forexample as used to produce dehydrated vegetables. Dehydration may be inhot air, or other forms of dehydration such as vacuum drying may beused. The cut may be dice, slices or julienne style strips. It ispreferred that the least (or shortest) dimension should not be more thanabout 5 mm.

Vegetable pieces are partially dehydrated to a moisture content of about8% to about 30%, preferably from about 8% to about 20%, more preferablyabout 8% to about 15%. At these moisture contents, the vegetable pieces,particularly when warm, are reasonably plastic. They are thencompressed, preferably by passing through a roller mill similar to thatused for flaking grains, or by other means known in the art such ashydraulically between flat plates. The rolls of a mill may be set at agap between about 0.2 mm to 2.5 mm. The roll gap will depend on thedimensions of the partially dehydrated piece. If the moisture content ofthe piece is too high, for example greater than 30%, the vegetable maysquash on to the rolls of the mill. If it is too dry, for example lessthan about 8%, it may shatter. The extent or fineness to which thevegetable is rolled will largely determine the cook time of the finishedproduct. If the piece is rolled too finely, the cook time will be almostinstant, but the texture may be mushy. The gap between the rolls will bedetermined by:

-   -   (i) thickness of the semi-dehydrated vegetable piece;    -   (ii) the type of vegetable and the variety;    -   (iii) the desired cook time;    -   (iv) the desired texture of the rehydrated product.

Vegetable pieces are compressed, preferably in one dimension, thecompression maintaining substantially intact cellular structure suchthat on rehydration, for example in water of 90° C. to 100° C., it iscapable of rehydration substantially to its original fresh (that isnon-dehydrated) dimensions over a period of up to five minutes.

Intact cellular structure may be determined in a conventional manner,such as by microscopy of a section.

Dried vegetables which have added solutes can also be prepared in thisway, for example, vegetables may contain added solutes in an amount from0.3% to 10% w/w. The introduction of sugars and salts is described, forexample, in Australian Patent No. 532414 or by other methods. Soluteswhich may be used include salts such as sodium chloride, sodium lactate,and sodium citrate, potassium lactate, or sugars (for example glucose,sucrose, fructose) and others known in the art such as sorbitol. Theaddition of solutes to the vegetables further accelerates the absorptionof water, shortens the cooking time, and may improve the plasticity ofthe pieces during compression.

After compression, the vegetable pieces will have been flattened to adegree depending on the reduction of cook time required. The vegetablepieces may then be further dehydrated to produce a shelf-stable product.Further dehydration results in the rapid loss of moisture since thecompressed product gives up its moisture very rapidly as compared to apiece which has not been compressed. The final moisture content shouldpreferably be of about 12% or lower, such as from about 2% to about 10%,for example, more preferably 4% to 6%.

The compression of the vegetables results in greatly decreasedrehydration time of the vegetable piece. Table 1 presents the effect ofcompression on rehydration time of compressed dehydrated vegetables withand without the addition of solutes, in this case of sodium chloride.

Table 2 shows the effect of the degree of compression during rolling onthe cook time and texture of dehydrated onion.

TABLE 1 Time required for dehydrated vegetables to stand in water at 90°to 100° C. to be sufficiently rehydrated and tender to be veryacceptable for eating. All vegetables compressed through 0.5 mm roll gapexcept peas which were rolled through a 1.5 mm gap. Vegetable Dimensionsare before 5% Solute dehydration Control Not Rolled Rolled Added RolledTomato 10 mm 8 mins 4 mins 2 mins peeled dice Onion 10 mm dice 10 mins 3 mins 1½ mins Red Bell Peppers 6 mins 1½ mins 1 min 8 × 8 mm dice SweetCorn 10 mins  4 mins 3 mins whole kernels Green Peas 8 mins 4 mins 3mins Carrot 6 mins 3 mins 2 mins 10 × 4 × 4 mm dice

TABLE 2 Effect of degree of compression on rehydration time of 10 × 10mm dehydrated onion dice containing 5% salt on standing in water at 90°to 100° C. Gap Between Rolls Rehydration Time Comments 0.3 mm below 1 mmRehydrated pieces mushy, did not re-hydrate to original fresh dimensions0.5 mm  1 mm Slightly mushy. Some loss of texture 0.8 mm  2½ mins Crispbut well rehydrated Unrolled control 10 mins Well rehydrated

By use of compression as described, varying cook times can be selectedfor vegetable pieces of almost instant, upwards. The cook time can bevaried for each vegetable by adjusting:

-   -   1. The initial size of the vegetable piece.    -   2. The degree of compression.    -   3. The addition of solutes.    -   4. The nature of the solutes added.

A further advantage of the compressed vegetables is that they have agreater tendency to float on the surface than traditional dehydratedvegetables. This is probably due to their lower bulk density.

Surprisingly unless compressed to an excessive degree the compressedvegetables exhibit surprisingly a marked ability to rehydrate to theinitial shape of the fresh vegetable piece.

EXAMPLE 1

Onions with a solids content of 14% were peeled and diced, 10×10 mmpieces were dehydrated in a hot air dryer at 70° C. to a moisturecontent of 15%. The partially dried pieces were compressed by passingthrough a roller mill with a gap of 0.5 mm. The semi-dried onions passedreadily through the mill without sticking or shattering. They were thenfurther dried at 60° C. to a moisture content of 5%. When placed in acup with boiling water poured over them, the pieces were sufficientlyrehydrated to consume after one and a half minutes.

EXAMPLE 2

Peeled carrots with a total solids content of 12% were diced into pieces10×4×4 mm. The pieces were steam blanched for one minute, then coatedwith sufficient salt solution to give a salt content in the finalproduct of 5% w/w. The carrot was dehydrated at 70° C. in a hot airdryer to a moisture content of 20%. The pieces were compressed bypassing through a roller mill with the gap set at 0.4 mm, and then driedfurther at 70° C. to 5% moisture.

When placed in a cup of boiling water and allowed to stand, the carrotpieces were quite tender and sufficiently rehydrated to eat after twominutes.

Dehydrated vegetables with rapid rehydration times can thus be producedby compressing partially dehydrated vegetables for example by passingthrough the gap of a roller-mill prior to final dehydration. Theincreased speed of rehydration can be further increased by thecompression of vegetables to which solutes have been added.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

1. A process for the preparation of a dehydrated, rapidly rehydrating,vegetable product which comprises: a) partially dehydrating vegetablepieces to a moisture content from about 8% to about 30%, b) prior tocompressing the vegetable piece in one dimension one or more solutes areadded to the piece, c) compressing the vegetable piece in one dimensionto about 0.2 to 2.5 mm, and d) thereafter further dehydrating thecompressed vegetable piece to a moisture content of about 12% or lower,wherein the vegetable piece when placed in water at a temperature of 90°C. to 100° C. without further application of heat is capable ofrehydration substantially to its original fresh dimension and is ofedible tenderness and texture instantly or within five minutes.
 2. Aprocess according to claim 1 wherein the vegetable is selected from thegroup consisting of carrots, peas, peppers, tomatoes, sweet corn, onion,squash, chillies, zucchini, mushroom, cabbage, celery, green beans,beetroot and pumpkin.
 3. A process according to claim 1 wherein saidsolutes are selected from the group consisting of sodium chloride,potassium chloride, sodium lactate, potassium lactate, sodium citrate,glucose, sucrose, fructose and sorbitol.
 4. A process according to claim1 wherein the compressed vegetable piece in step d) is dehydrated to amoisture content from about 2% to about 12%.
 5. A process according toclaim 4 wherein the vegetable piece is dehydrated to a moisture contentfrom 4% to 6%.
 6. A process according to claim 1 wherein said vegetablepiece is compressed in a roller mill.
 7. A process according to claim 1wherein said added solutes are present in an amount from 0.3% to 10%w/w.
 8. A process according to claim 1 wherein the vegetable piece isdehydrated in step a) to a moisture content which is from about 8% toabout 20%.